A selectively permeable membrane type reactor (also called “membrane reactor”; see patent document 1) is a new concept reactor which includes a catalyst for promoting a chemical reaction and a selectively permeable membrane which selectively allows a specific component to pass therethrough to exhibit a catalytic effect and selective permeability. For example, a selectively permeable membrane type reactor called an extractor type reactor simultaneously effects a chemical reaction using the catalyst and separation/recovery of the reaction product using the selectively permeable membrane, and has been used for producing hydrogen by reforming a hydrocarbon and separating/recovering the produced hydrogen. In recent years, hydrogen has attracted attention as a clean energy source in the field of fuel cells and the like. Therefore, this type of reactor is expected to be increasingly used in the future.
As a known selectively permeable membrane type reactor, a selectively permeable membrane type reactor 10 shown in FIG. 1 has been widely used which has a double tube structure having a reaction tube 2 and a separation tube 4 with a bottom which is disposed inside the reaction tube 2 and formed of a porous body, in which a catalyst 6 for promoting a chemical reaction is disposed in the space between the reaction tube 2 and the separation tube 4, and a selectively permeable membrane 8 which selectively allows a specific component to pass therethrough is disposed on the outer surface of the separation tube 4.
The configurations of the catalyst and the selectively permeable membrane of the selectively permeable membrane type reactor 10 differ depending on the application (type of reaction). In an extractor type reactor used for producing hydrogen by reforming a hydrocarbon and separating/recovering the produced hydrogen, a nickel (Ni) or ruthenium (Ru) based reforming catalyst which promotes a reforming reaction of a hydrocarbon is provided as the catalyst 6, and a hydrogen permeable membrane formed of a palladium-silver (Pd—Ag) alloy and a ceramic porous body made of a silica (SiO2) or zirconia (ZrO2), which selectively allows hydrogen to pass therethrough, is provided as the selectively permeable membrane 8, for example.
According to the selectively permeable membrane type reactor 10, when a raw material gas G1, such as a hydrocarbon (methane in this example) and steam, is introduced through a gas inlet 2a of the reaction tube 2 at a high temperature of about 300 to 1000° C., the raw material gas G1 contacts the catalyst 6, whereby a reforming reaction shown by the following formula (1) and a shift reaction shown by the following formula (2) are promoted. This catalytic effect causes the hydrocarbon (methane) to be decomposed into reaction products such as hydrogen, carbon monoxide, and carbon dioxide, whereby a mixed gas (product gas) containing these reaction products is obtained.CH4+H2O⇄CO+3H2  (1)CO+H2O⇄CO2+H2  (2)
The hydrogen obtained as the product gas passes through the selectively permeable membrane 8 to enter the separation tube 4 formed of the porous body, and is separated/recovered as a permeable gas G2 through an open end 4a of the separation tube 4. On the other hand, since the remaining components (e.g. carbon monoxide and carbon dioxide as the reaction products and unreacted raw material gas) cannot pass through the selectively permeable membrane 8, these components pass through the reaction tube 2 and are recovered as an impermeable gas G3 through a gas recovery port 2b. This mechanism allows the permeable gas G2 and the impermeable gas G3 to be separated and individually recovered, whereby only the target component (hydrogen in this example) can be selectively separated/recovered from the reaction products of the reforming reaction.
Since the selectively permeable membrane type reactor can achieve catalytic reaction promotion and selective permeation of a specific component using the selectively permeable membrane by a series of operations in a single reactor, the selectively permeable membrane type reactor has a compact configuration and requires only a small installation area. Moreover, since part of the reaction products passes through the selectively permeable membrane and is removed from the reaction system, the chemical reaction equilibrium shifts toward the production side, whereby a reaction can take place at a low temperature. Therefore, consumption of energy supplied from the outside during the reaction can be reduced, and deterioration and corrosion of the reactor can be prevented. This makes it unnecessary to use an expensive heat-resistant/corrosion-resistant material as the material for the reactor, whereby the cost of the reactor can be reduced.
[Patent document 1] JP-A-6-40703